A photo interrupter and a method of manufacturing the same

Abstract: A photo interrupter includes a lead frame having a light-emitting element and a light-receiving element provided thereon and having a lead pattern for connecting input/output terminals of both the light-emitting element and said light-receiving element to the outside at a converged connector-jointing portion. Both the light-emitting element and the light-receiving element are provided on the common lead frame which is connected directly to a connector for connecting to the outside. A casing for holding the light-sensing parts is composed of a thermoplastic resin and provided with melt pins joining the connector and the lead frame to the casing.

Description: BACKGROUND OF THE INVENTION (1) Field of the Invention The present invention relates to a photo interrupter in which a light-emitting element and a light-receiving element are disposed opposing each other to create an object passage whereby an object which passes therebetween is detected. (2) Description of the Prior Art Fig.1 is a constructional example of a prior art photo interrupter. The construction of this photo interrupter will be explained in the following steps of the manufacturing procedure. A light-emitting-side transparent resin part 60 is formed such that a light-emitting element, after mounted on a frame for a light-emitting element and bonded thereon, is molded with a light transmissive resin material. Similarly, a light-receiving-side transparent resin part 61 is formed such that a light-receiving element, after mounted on a frame for a light-receiving element and bonded thereon, is molded with a light transmissive resin material. A lead 60a from the light-emitting-side transparent resin part 60 and leads 61a and 61b from the light-receiving-side transparent resin part 61 are soldered on a print board 62 so as to form a passage 63 to allow an object to pass through. A connector 64 for electrically connecting the light-emitting element and light-receiving element with the outside is fixedly joined with solder 65 to the print board 62. After checking the soldering, the print board 62 is fitted into a casing 66 having hooks 66a and 66b in the bottom thereof. These hooks 66a and 66b are used to assure the fixing between the print board 62 and the casing 66 itself. As stated above, many components, e.g. the light-emitting-side transparent resin part 60, the light-receiving-side transparent resin part 61, the print board 62, the connector 64 and the casing 66 as in the above case, have been required for such a conventional photo interrupter. For this reason, the prior art devices disadvantageously took much time and labor for assembling. Further, there were quite a few places to be soldered in assembling; therefore, examination of the soldering was required to maintain reliability and quality. Since the connection between the print board 62 and the connector 64 is supported by the strength of the solder, reliable and rigid soldering is required. A photo interrupter similar to the photo interruptor shown in Figure 1 is disclosed in JP-A-63 236 374, on which the preambles of claims 1 and 5 are based. Further, fastenings with complicated structures such as hooks 66a, 66b were used for fixing, so that the work not only took much time and labour but also involved a high likelihood of damage ocurring. According to a first aspect of the present invention there is provided a photo interrupter comprising: a light-emitting element; a light-receiving element; a lead frame having both said light-emitting element and said light-receiving element provided thereon; a connector connected to said lead frame; and a casing covering said light-emitting element, said light-receiving element and said lead frame; the photo interrupter being characterised in that the lead frame has first, second and third terminals disposed adjacent to one another, and has a lead pattern for connecting the input and output terminals of the light-emitting element and the light-receiving element to the terminals of the lead frame; and in that the connector is connected to the terminals of the lead frame. Preferred features of a photo interrupter of this invention are set out in dependent claims 2 to 4. According to a second aspect of the present invention there is provided a method of manufacturing a photo interrupter comprising the steps of: providing a light-emitting element and a light-receiving element on a lead frame; moulding said elements with a light transmissive resin: bending said lead frame so that said light-emitting element and said light-receiving element are opposed to each other; connecting a connector to said lead frame: holding said lead frame with said connector connected in a casing; and joining said lead frame with said casing by heat-pressing; characterised in that the lead frame has first, second and third terminals disposed adjacent to one another and a wiring pattern for connecting the input and output terminals of the light-emitting element and the light-receiving element to the terminals of the lead frame; in that the light-emitting element and the light-receiving element are moulded with the light transmissive resin simultaneously; and in that the connector is connected to the lead frame by welding. Thus, the photo interrupter of the present invention, both the light-emitting element and the light-receiving element are provided on the common lead frame. Since this lead frame has a lead pattern for connecting input/output terminals of both the light-emitting element and the light-receiving element to the outside at a converged connector-jointing portion, a complete electric connection for the photo interrupter can be done by only connecting a connector to the connector-jointing portion in the lead frame in which the light emitting element and the light-receiving element are provided. In this way, the lead frame with the light-emitting element and light-receiving element provided thereon has a complete lead pattern to the connector, therefore, it is possible to directly joint the connector to the lead frame, resulting in reduced places to be interconnected. In the photo interrupter of the present invention, the connector is joined to the casing, so that the connector is supported by the casing. An increased number of points for supporting makes the holding state rigid. In the photo interrupter of the present invention, since the joint portions are composed of a thermoplastic resin, it is possible to easily join the thermoplastic resin part with the other parts (such as the lead frame and the connector) by heat-pressing. In the photo interrupter of the present invention, since the lead frame is composed of a conductive material having rust-resistance, no plating for providing rust-resistance is required for the lead frame. Since the connection between the lead frame and the connector is done by welding, any plating which would have been required for soldering is unnecessary. In the case of the conventional photo interrupter requiring a print board, since the print board has an insulating layer on the surface thereof, it is impossible to weld the board with a connector. That is, in the present invention, the integration of the lead frame enables welding connection, whereby it is possible to omit the plating of the lead frame. On the other hand, in accordance with the method of manufacturing a photo interrupter of the present invention, a light-emitting element and a light-receiving element are both provided on a single lead frame and molded with a resin. The thus formed lead frame is bent, jointed with a connector and housed by a casing. In the course of the operation steps, since both the light-emitting element and the light-receiving element are processed as provided on the lead frame, work steps such as molding, interconnecting etc. can be reduced. Since the lead frame used here has a converged site on one side for collecting the input/output terminals of the light-emitting element and the light-receiving element, it is possible to join the lead frame with the connector at the converged site all at once. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a sectional view showing a configuration of a prior art photo interrupter; Fig.2A is a plan view showing a configuration of a photo interrupter in accordance with an embodiment of the present invention; Fig.2B is a front view showing a configuration of a photo interrupter in accordance with an embodiment of the present invention; Fig.2C is a bottom view showing a configuration of a photo interrupter in accordance with an embodiment of the present invention; Fig.2D is a right-side view showing a configuration of a photo interrupter in accordance with an embodiment of the present invention; Fig.2E is a perspective appearance view showing a configuration of a photo interrupter in accordance with an embodiment of the present invention; Fig.3 is a plan view showing lead frames built in with light-emitting elements and light-receiving elements; Fig.4 is a plan view showing lead frames with light-emitting elements and light-receiving elements molded; Fig.5 is a plan view showing lead frames after unnecessary parts are removed by die cutting; Fig.6A is a plan view showing a lead frame built in with a light-emitting element and a light-receiving element; Fig.6B is a front view showing a lead frame built in with a light-emitting element and a light-receiving element; Fig.6C is a diagram showing an equivalent circuit to the photo interrupter shown in Figs.6A and 6B; Fig.7 is a perspective view showing a state in which the light-emitting element portions and light-receiving element portions shown in Fig.6A are bent upright so as to oppose each other; Fig.8 is a perspective view showing a state of a photo interrupter with a connector fixed; Fig.9 is a plan view showing a state of a photo interrupter with a connector fixed; Fig.10 is a sectional view showing a configuration of a casing; and Fig.11 is a sectional view showing a configuration of a photo interrupter in accordance with an embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will hereinafter be described with reference to the accompanying drawings. Figs.2A to 2E are views showing a photo interrupter in accordance with an embodiment of the present invention. Figs.2A, 2B, 2C and 2D are plan, front, bottom and right-side views of the embodiment, respectively. Fig.2E is a perspective appearance view of the same embodiment. Figs.3 through 10 are views of the features of parts of the same photo interrupter and the states under manufacturing the same. In Figs.2A through 2E, a light-emitting portion 2 and a light-receiving portion 3 are housed by a casing 5 and disposed opposing each other with an object passage 6 in between. A connector 4 is provided projected from the side of the light-emitting portion 2. The configuration of this photo interrupter will be now described in the following steps of the manufacturing procedure. Fig.3 is a view showing a lead frame on which light-emitting elements and light-receiving elements are provided. A lead frame 1 is composed of a nickel alloy (e.g., 42 alloy) having a high strength and rust-resistance. Use of a nickel alloy material provides a good weather resistance for the lead frame without necessity of rust-resistance plating on the surface of the lead frame. A light-emitting element 21 as well as a light-receiving element 31 is provided on each lead frame 1 (for one photo interrupter), fixed and wire-bonded. The structure of the lead portion in the lead frame 1 will be further described later. After the light-emitting element 21 and the light-receiving element 31 have been bonded as stated, the elements 21 and 31 are molded as shown in Fig.4 with a transparent resin (mold resin 22 and 32). At the time, the elements 21 and 31 are designed to be provided on the common frame in the present invention, unlike the prior art configuration in which the light-emitting element and the light-receiving element are provided separately, therefore, it is possible to mold both the elements 21 and 31 at a single step. Accordingly, operation steps can be reduced in number and process cost as well as material cost can be reduced. Thereafter, the lead frame 1 is die-cut (by tie bar cut), unnecessary parts being removed as shown in Fig.5, so as to be checked on performances and characteristics. Referring now to Figs.6A to 6C, the construction of the lead frame 1 will be described. Figs.6A and 6B are plan and front views showing the lead frame with the light-emitting element and light-receiving element provided. Fig.6C is a diagram showing an equivalent circuit to the photo interrupter. In Fig.6A, chained lines indicate bending lines along which the frame is bent upright so that molded resin portions 22 and 23 of the light-emitting element and the light-receiving element are opposed to each other. Reference numerals 41a to 43a with hatching designate connecting parts to be connected to pins 41b to 43b of the connector 4, which will be detailed later. The connecting parts in this embodiment are brought together on the side of the light-emitting portion 2. Here, the connecting parts 41a to 43a may be formed on the light-receiving side or in any other site as long as they are gathered so that the connector 4 can be joined at one place. Although an LED is used as the light-emitting element and a photo transistor is used as the light-receiving element in this specific embodiment, other device elements may be used. For example, a photodiode or photo IC is applicable as the light-receiving element. In the case, the parts should be arranged in such a manner that input/output terminals of the light-emitting element and the light-receiving element can be connected to a single connector. A collector terminal 33 of the light-receiving element 31 is connected to the connecting part 41a for outputting a detection signal to the connector. The emitter terminal 34 is connected to the connecting part 42a for ground in the connector as well as to a cathode terminal 23 of the light-emitting element 21 via a wire. In this embodiment, although the emitter terminal 34 is wire-connected with the cathode terminal 23, the connection may be done through the lead frame itself. An anode terminal 24 of the light-emitting element 21 is connected to the connecting part 43a for input. A base terminal 35 of the light-receiving element 31 is open. Next, a bending step follows. The lead frame is bent along the chained lines shown in Fig.6A as required, so that the light-emitting element 21 and the light-receiving element 31 are made upright opposing each other as shown in Fig.7. In this case, the outmost leads and the connecting part 42a for ground will not be bent. Thus, a light sensing part composed of the light-emitting portion and the light-receiving portion is completed. Subsequently, the connecting pins 41b to 43b are mated with the connector parts 41a to 43a, respectively, so that the lead frame 1 is joined to the connector 4. In this embodiment, this joint is performed by spot-welding. As a result, the connecting work is markedly simplified because there is no need for plating the lead frame 1 for soldering, not to mention, the adjustment of the amount of soldering material etc. The state of the connector fixed is shown in Figs.8 and 9. As apparent from the manufacturing steps heretofore, since both the light-emitting element 21 and the light-receiving element 31 is provided on the common lead frame 1 having connecting parts to be joined to the connector, no print board used in the prior art configuration (designated at 62 in Fig.1) is needed, therefore, there is no need for either setting or soldering of the light-emitting-side transparent resin part (60) and the light-receiving-side transparent resin part (61) onto the print board 62. Further, since the use of the lead frame in the invention enables the light sensing part to be joined to the pins 41b to 43b of the connector 4 by welding, this can not only simplify the connecting work but also improve physical strength and thermal resistance of the device. Next, the light sensing part including the lead frame 1 is assembled into the casing 5. Fig.10 shows a sectional structure of the casing 5. This casing 5 is formed of a molding with a colored thermoplastic resin so as to block light, and has a light-emitting-element holding portion 5a and a light-receiving-element holding portion 5b both resin-molded. The holding portions 5a and 5b for a light-emitting element and a light-receiving element have windows 53, 54 respectively, in order to allow light beams to be emitted and received between the light-emitting element 21 and the light-receiving element 31. Provided in the middle on the underside of the casing 5 are a pair of melt pins 51. These melt pins 51 are fitted into holes (11 in Fig.6A) in the lead frame 1, thereafter, pressed with heat, whereby the casing 5 is fixed to the lead frame 1. Another set of melt pins 52 is provided for the casing 5 on the edge to which the connector 4 is jointed. After fitted into the gaps between connecting parts 41a, 42a and 43a for the connector, the melt pins 52 are heat-pressed and fixed. This further makes firm the joint between the lead frame 1, the connector 4 and the casing 5. Here, although the entire part of the casing is formed with a thermoplastic resin in this embodiment, only the melt pins 51 and 52 are essential part to be made from thermoplastic resin, and all the other part can be formed of the other kind of resin. For instance, a thermoplastic resin is used for forming the melt pins only while the other part of the casing may be formed of another resin having resistance to heat. In this manner, assembly of the photo interrupter is completed. Fig.11 shows a sectional configuration of the assembled photo interrupter of the present invention. In the figure, reference numerals 51' and 52' denote the melt pins which have been heat-pressed. In the above embodiment, the fixture between the casing 5 and the lead frame 1 as well as the fixture among the casing 5, the lead frame 1 and the connector 4 are done by the heat-pressing using a thermoplastic resin, but these joints can be done with an adhesive unless the casing is composed of any thermoplastic resin. Further, it is possible to use a thermoplastic resin for forming the melt pins only while the other part of the casing may be formed with another resin without thermoplasticity. As has been described, according to the present invention, since the light-emitting element and the light-receiving element are provided on a common single lead frame and the lead frame has a complete interconnecting pattern inclusive of the connecting parts for the connector, it is possible to markedly reduce the number of parts for assembly and therefore to reduce the steps of assembling. As an example, there is no more need for either mounting or soldering the light-emitting-side transparent resin body and the light-receiving-side transparent resin body onto the print board. Further, the reduction in the number of places to be soldered contributes to simplifying the visual check of the assembly. Further, according to the present invention, since the connector is jointed also to the casing, the connector can be held more firmly than in the conventional configuration in which the connector is held only by the lead frame. This feature contributes to preventing the connected portion between the lead frame and the connector from being bent or broken. Still more, according to the present invention, since the joint between the casing and the lead frame as well as the joints with the outside parts such as the connector is performed by heat-pressing using a thermoplastic resin, there is no need to provide any joint or fastening with a complicated structure such as hooks etc. Therefore, the structure of the joint portions can be simplified. Since there is no joint using fitting such as hooks etc. but, all the joints are performed by heat-pressing, the jointing can be quite simplified. Moreover, according to the present invention, since no plating treatment is required for jointing the lead frame with the connector or for providing rust-resistance for the parts, the plating treatment during manufacturing can be omitted. Finally, according to the present invention, it is possible to provide both the light-emitting element and the light-receiving element on the common lead frame having interconnecting patterns and mold them at the same time so that the different steps such as molding, interconnecting can be done together. Therefore, it is possible to improve work efficiency as well as to reduce the number of the processing apparatuses used. As to the connection of the lead frame with the connector, the connecting terminals are collected in a single site on one side of the lead frame, resulting in improved workability.

Claims: A photo interrupter comprising: a light-emitting element (21); a light-receiving element (31); a lead frame (1) having both said light-emitting element (21) and said light-receiving element (31) provided thereon; a connector (4) connected to said lead frame; and a casing (5) covering said light-emitting element, said light-receiving element and said lead frame; the photo interrupter being characterised in that the lead frame has first, second and third terminals 41a, 42a, 43a disposed adjacent to one another, and has a lead pattern for connecting the input and output terminals of the light-emitting element and the light-receiving element to the terminals of the lead frame; and in that the connector is connected to the terminals of the lead frame. A photo interrupter as claimed in claim 1 wherein said casing comprises joint portions for joining said casing with said connector. A photo interrupter as claimed in claim 1 or 2, wherein the casing (5) comprises joint portions consisting of a thermoplastic resin. A photo-interrupter as claimed in any of claims 1, 2 or 3, wherein the lead frame consists of a conductive and rust resistant material. A method of manufacturing a photo interrupter comprising the steps of: providing a light-emitting element (21) and a light-receiving element (31) on a lead frame; moulding said elements with a light transmissive resin; bending said lead frame so that said light-emitting element and said light-receiving element are opposed to each other; connecting a connector to said lead frame; holding said lead frame with said connector connected in a casing; and joining said lead frame with said casing by heat-pressing; characterised in that the lead frame has first, second and third terminals (41a, 42a, 43a) disposed adjacent to one another and a wiring pattern for connecting the input and output terminals of the light-emitting element and the light-receiving element to the terminals of the lead frame; in that the light-emitting element and the light-receiving element are moulded with the light transmissive resin simultaneously; and in that the connector is connected to the lead frame by welding.

Inventors: HORINOUCHI TERUHIKO, ONO NOBUMASA, HORINOUCHI, TERUHIKO, ONO, NOBUMASA
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1994
Main classification: H01L31
IPC codes: H01L31, H03K17